dec2hex.php

<?php

// Helpers
$space = function($hex) {
    return implode(' ', str_split($hex, 2));
};
$debug = function($dec) use ($space) {
    echo 'dec: ' . $dec . "\n";
    echo 'hex: ' . $space(dec2hex($dec)) . "\n\n";
};

// Cases
$_time = microtime(1);

$debug('2000'); // 2k
$debug('1000000'); // 1M
$debug('99999999'); // 100M
$debug('120045041395046077749311747456482878735'); // 12BBBB

// gmp is twice as fast as bc, but bc always works
echo number_format((microtime(1) - $_time) * 1000, 3) . "ms\n";



// Magic
function dec2hex($dec) {
    $bytes = 1;
    while (gmp_cmp(gmp_pow(256, $bytes), $dec) <= 0) {
    #while (bccomp(bcpow(256, $bytes), $dec) <= 0) {
        $bytes++;
    }

    $left = gmp_init($dec);
    #$left = $dec;

    $bin = '';
    for ($byte = $bytes; $byte > 0; $byte--) {
        $range = gmp_pow(256, $byte-1);
        #$range = bcpow(256, $byte-1);

        $n = gmp_div($left, $range);
        #$n = bcdiv($left, $range, 0);

        $left = gmp_sub($left, gmp_mul($range, $n));
        #$left = bcsub($left, bcmul($range, $n));

        $bin .= chr(gmp_strval($n));
        #$bin .= chr($n);
    }

    return bin2hex($bin);
}